Multi-protocol Label Multi-protocol Label SwitchingSwitching

-Presented By-Presented ByAyan Kumar RoyAyan Kumar Roy

Roll No. 05IT6020Roll No. 05IT6020M. Tech (IT), I.I.T, KGPM. Tech (IT), I.I.T, KGP

School of Information TechnologySchool of Information Technology

Under Guidance ofUnder Guidance ofDr. S.K.GhoshDr. S.K.Ghosh

MPLS Introduction Motivation MPLS Basics Components and Protocols Operation Advantages and Disadvantages

Motivation IP

The first defined and used protocol De facto the only protocol for global

Internet working

… but there are disadvantages

Motivation (cont.) IP Routing disadvantages

Connectionless- e.g. no QoS

Each router has to make independent forwarding decisions based on the IP-address

Large IP Header- At least 20 bytes

Routing in Network Layer- Slower than Switching

Usually designed to obtain shortest path- Do not take into account additional metrics

Motivation (cont.) ATM

connection oriented- Supports QoS

fast packet switching with fixed length packets (cells)

integration of different traffic types (voice, data, video)

… but there are also disadvantages

Motivation (cont.) ATM disadvantages

Complex Expensive Not widely adopted

Motivation (cont.) Idea: Combine the

forwarding algorithm used in ATM with IP.

MPLS Introduction Motivation MPLS Basics Components and Protocols Operation Advantages and Disadvantages

MPLS Basics Multi Protocol Label Switching is

arranged between Layer 2 and Layer 3

MPLS Basics (cont.) MPLS Characteristics

Mechanisms to manage traffic flows of various granularities (Flow Management) such as flows among different hardware, machines, or even flows among different applications.

Is independent of Layer-2 and Layer-3 protocols Maps IP-addresses to fixed length labels Interfaces to existing routing protocols (such as

RSVP, OSPF) supports the IP, ATM, and frame-relay Layer 2

protocols.

MPLS Introduction Motivation MPLS Basics MPLS Components and

Protocols MPLS Operation Advantages and Disadvantages

Label Edge Router - LER

Resides at the edge of an MPLS network and assigns and removes the labels from the packets.

Support multiple ports connected to dissimilar networks (such as frame relay, ATM, and Ethernet).

Label Switching Router - LSR

Is a high speed router in the core on an MPLS network.

ATM switches can be used as LSRs without changing their hardware. Label switching is equivalent to VP/VC switching.

Position of LERs and LSRs

Label

A label is a short, fixed-length value carried in the packet's header to identify a forwarding equivalence class (FEC).

A label is analogous to a connection identifier, such as an ATM VPI/VCI or a Frame Relay DLCI, because it has only link-local significance, does not encode information from the network layer header, and maps traffic to a specific FEC.

Label

Generic label format

Label Creation

Topology-based method – uses normal processing of routing protocols (such as OSPF and BGP)

Request-based method – uses processing of request-based control traffic (such as RSVP)

Traffic-based method – uses the reception of a packet to trigger the assignment and distribution of a label

The topology- and request-based methods are examples of control-driven label bindings, while the traffic-based method is an example of data-driven binding

Label (cont.) Label distribution

MPLS does not specify a single method for label distribution

BGP has been enhanced to piggyback the label information within the contents of the protocol

RSVP has also been extended to support piggybacked exchange of labels.

IETF has also defined a new protocol known as the label distribution protocol (LDP) for explicit signaling and management

Forward Equivalence Class - FEC

Is a representation of a group of packets that share the same requirements for their transport.

The assignment of a particular packet to a particular FEC is done just once (when the packet enters the network).

Label-Switched Paths -LSPs Within an MPLS domain, a path is

set up for a given packet to travel based on an FEC.

The LSP is set up prior to data transmission.

LSP Details MPLS provides two options to set up an LSP

hop-by-hop routingEach LSR independently selects the next hop for a given FEC. LSRs support any available routing protocols (OSPF, ATM …).

explicit routingIs similar to source routing. The ingress LER specifies the list of nodes through which the packet traverses.

The LSP setup for an FEC is unidirectional. The return traffic must take another LSP!

MPLS Introduction

Motivation MPLS Basics Components and Protocols Operation Advantages and Disadvantages

MPLS Operation

The following steps must be taken for a data packet to travel through an MPLS domain. label creation and distribution table creation at each router label-switched path creation label insertion/table lookup packet forwarding

MPLS Operation Example

Packet Forwarding

Packet forwarding LER1 may not have any labels for this

packet as it is the first occurrence of this request. In an IP network, it will find the longest address match to find the next hop. Let LSR1 be the next hop for LER1.

LER1 will initiate a label request toward LSR1.

This request will propagate through the network as indicated by the broken green lines.

Packet Forwarding (cont.)

Each intermediary router will receive a label from its downstream router starting from LER4 and going upstream till LER1.

All these routers will update their LIB table for this FEC.

The LSP setup is indicated by the broken blue lines using LDP or any other signaling protocol.

LER1 will insert the label and forward the packet to LSR1.

Example of LIB Table

Input PortIncoming Port Label

Output Port

Outgoing Port Label

1 3 3 6

2 9 1 7

Packet Forwarding (cont.)

Each subsequent LSR, i.e., LSR2 and LSR3, will examine the label in the received packet, replace it with the outgoing label and forward it.

When the packet reaches LER4, it will remove the label because the packet is departing from an MPLS domain and deliver it to the destination.

The actual data path followed by the packet is indicated by the broken red lines.

MPLS Operation Example

Packet Traversing a Label-Switched Path

MPLS Introduction

Motivation MPLS Basics Components and Protocols Operation Advantages and Disadvantages

MPLS Introduction Motivation Basics Components and Protocols Operation Advantages and Disadvantages

MPLS Advantages

Improves packet-forwarding performance in the network

Supports QoS and CoS for service differentiation

Supports network scalability Integrates IP and ATM in the network Builds interoperable networks

MPLS Disadvantages An additional layer is added The router has to understand MPLS

References http://www.iec.org/online/tutorials/mpls.pdf Cisco Press-Network Consultants Handbook-by Math

ew Castelli.pdf http://www.iaik.tugraz.ac.at/teaching/03_advanced

%20computer%20networks/ss2004/vo3/MPLS.pdf by Mario Ivkovic

http://ica1www.epfl.ch/cn2/0304/doc/lecture/mpls.pdf

Encyclopedia of Netwoking.pdf

MPLS Introduction

Q & A

MPLS Introduction

Thank you!